1. Field of the Invention
This invention relates to a method for insulating a body of water against heat loss. More particularly, this invention relates to a method for reducing evaporation and heat loss from a contained body of water by generating a layer of cured organopolysiloxane foam on the surface of the water.
2. Description of the Prior Art
There is an ongoing need for new sources of energy other than fossil fuels. One alternative source that has been the subject of much investigation is utilization of the heat energy imparted to contained bodies of water by the sun. This heat energy can be removed from the water by heat exchangers and subsequently converted to other forms, such as electricity, by the use of turbine-driven devices, including generators. While it is true that certain contained bodies of water, referred to in the art as solar ponds, absorb and retain solar energy as heat, this advantage is offset by the tendency of the water to radiate a substantial portion of this stored energy back into the atmosphere when the sun is not present. One method for reducing this heat loss is to employ what has become known as a salt gradient pond, in which a higher concentration of dissolved salt is established throughout the lower portion of the pond than at the surface. The higher salt content at the lower levels reduces or prevents thermal convection whereby the heated water at the bottom of the pond would tend to rise to the surface and lose its heat to the atmosphere through evaporation. While salt gradient ponds are initially relatively efficient, the salt gradually diffuses throughout the entire pond, thereby nullifying the ability of the pond to suppress convective heat loss. The salt gradient can be reestablished by injection of a concentrated salt solution at the bottom of the pond and addition of fresh water to the surface layer.
An alternate method for reducing convective and evaporative heat losses from solar ponds is to employ a fresh water pond having an insulating layer over the surface of the pond. In addition to reducing heat loss and evaporation, the layer should be sufficiently transparent or translucent to allow at least a portion of the incident sunlight to penetrate the layer and warm the surface of the pond. A variety of insulative materials, including floating glass beads, inflated multiple plastic films, liquid foams, blocks of previously prepared solid foam and removable covers have been proposed, however none of these has proven completely satisfactory.
Generating a solid, curable foam on the surface of the water would provide the desired insulation against heat loss as well as reduce evaporation. Organopolysiloxane foams would be particularly desirable because of their durability and chemical inertness, however the prior art does not teach a method for generating this type of foam in the presence of a large excess of water.
Organopolysiloxane foams are well known materials. U.S. Pat. No. 3,024,210, issued on Mar. 6, 1962 to Donald E. Weyer, discloses a method for forming organopolysiloxane resin foams at room temperature and states that these types of foams are useful as insulating materials for a variety of substrates. The foams are prepared by reacting an organopolysiloxane containing at least 1% by weight of SiH groups and a non-acidic hydroxylated compound, such as water, in the presence of a catalytic amount of a quaternary ammonium compound. The concentration of hydroxylated compound is preferably less than 50%, based on the weight of the organopolysiloxane.
The use of platinum compounds as catalysts for the reaction between compounds containing terminal silicon-bonded hydrogen atoms and hydroxyl-containing compounds is taught in U.S. Pat. No. 3,458,469, issued on July 29, 1969 to R. A. Murphy, which further discloses forming solid, "bubble-free, transparent" elastomers by reacting silicon-hydrogen terminated organopolysiloxanes with silanol terminated organopolysiloxanes at room temperature in the presence of a platinum catalyst and an organosilicon compound containing more than two silicon-bonded hydrogen atoms per molecule. Since the objective of this teaching is to prepare "bubble-free" products, using the hydrogen generated as a by-product of the reaction as a blowing agent to form a foam material would be directly contrary to the teaching of this reference.
U.S. Pat. No. 3,923,705, issued on Dec. 2, 1975 to S. B. Smith is directed toward a method for preparing fire retardant siloxane foams by the reaction of an organohydrogen siloxane, a hydroxylated organosiloxane and a platinum catalyst. This reference specifies that the molar ratio of silicon-bonded hydrogen atoms to silicon-bonded hydroxyl radicals is from 2.5 to 40. Below a ratio of 2.5, the foams "are too friable and weak to be useful in the known applications."
The use of rhodium compounds as catalysts for the preparation of organopolysiloxane foams by the reaction of an organohydrogensiloxane with a hydroxyl-containing organosiloxane is taught in U.S. Pat. No. 4,026,835 issued on May 31, 1977 to C. L. Lee et al. The reaction is conducted at temperatures of at least 90.degree. C., which would not be applicable to preparing foams at the ambient temperature of a body of water.
None of the aforementioned references provides a practical method for forming a cured organopolysiloxane foam on the surface of a body of water using the water as one of the reactants. Applicants have found that this objective can be achieved by covering the surface of a contained body of water with a composition containing at least one member of a specified class of liquid organohydrogenpolysiloxanes having a concentration of silicon-bonded hydrogen atoms that is within a specified range, and an effective amount of a catalyst that will promote the reaction of the organohydrogenpolysiloxane with water at the desired rate under ambient conditions to yield a cured foam. Formation of a cured foam from an organohydrogenpolysiloxane in the presence of so large an excess of water is considered surprising in view of the teaching in the aforementioned patents.